As for walls of residential houses and buildings and bodies of automobiles, coating films are often formed on their surfaces in order to protect their appearances or provide glories. Such the coating films are degraded gradually due to the effects of sun light, water, changes in ambient temperature or the like during exposure to the outdoors for long time and their appearances deteriorate.
The degradation of the coating film is generally evaluated as weather resistance. This evaluation of the weather resistance is conducted by exposing the coating films in Okinawa in Japan or Florida in USA. In these areas, it is hot and wet and an amount of ultraviolet light is much, and the environment is harsh for coating films. Since such exposure requires much time, various accelerated weathering testers have been developed as an apparatus capable of evaluating weather resistance in a short time.
However, in the previous accelerated weathering testers, some coating films, which were considered to have adequate weather resistance by a test, actually caused problems such as cracks or discoloration with time and its correlation with the results of actual exposure was not insufficient. And, the test in which the conventional accelerated weathering testers are used has an acceleration factor of about 10 to 100 times, and an accelerated weathering tester, which can conduct the test at higher acceleration factor, has been desired.
On the other hand, in a conventional accelerated weathering tester, loads applied to coating films for the accelerated degradation are limited to factors such as ultraviolet light, water and changes in ambient temperature, given from nature, and there were few attempts to apply another factors.
In Japanese Kokai Publication Hei-9-178727, there is disclosed a test method of organic materials, an accelerated degradation of coating films is conducted using a plasma generating apparatus of a type having parallel plate type electrodes in this patent. However, there is no clear description on a correlation with the results of natural exposure. Further, in the case where a coating film is formed on a metal material, when plasma is irradiated directly to the coating film using such an apparatus, a metal portion must be masked because spark-discharge may be generated to destroy the material, and in addition it is difficult to keep a constant test conditions because the temperature of the coating film is raised due to the occurrence of induction heating by a high-frequency. On the other hand, in the case where a coating film is formed on a porous inorganic material such as a ceramic board, there was a problem that a volatile ingredient from the inorganic material had an effect on test results in a high-vacuum condition in which plasma is irradiated.
When in order to resolve such the problems, the present inventors studied the results of natural exposure tests in detail, it was recognized that the degradation of coating films in natural exposure proceeded based on the degradation of the surface layer in the surface of a coating film. On the contrary, in the conventional accelerated weathering tester, it became apparent that the degradation of a deep layer simultaneously occurs. It is supposed that an adequate correlation with the results of the natural exposure cannot be obtained due to such the different points.
If a usual plasma generating apparatus, which is described in Japanese Kokai Publication Hei-9-178727, is employed, it is impossible to selectively develop only the degradation of the surface layer and to resolve the problems described above.